<template>
  <div id="page">
    <myHead></myHead>
    <div style="padding-top: 62px">
      <router-view></router-view>
      <div class="backTop" v-show="btnFlag" @click="backTop"></div>
    </div>
  </div>
</template>

<script>
    import myHead from './TopHeader';
    export default {
        name: 'page',
        components: {myHead},
        data () {
            return {
                btnFlag: false
            }
        },
        created(){
            // vue的两个生命钩子，这里不多解释。
            // window对象，所有浏览器都支持window对象。它表示浏览器窗口，监听滚动事件
            window.addEventListener('scroll', this.scrollToTop)
        },

        destroyed () {
            window.removeEventListener('scroll', this.scrollToTop)
        },
        methods: {
            // 点击图片回到顶部方法，加计时器是为了过渡顺滑
            backTop() {
                const that = this
                let timer = setInterval(() => {
                    let ispeed = Math.floor(-that.scrollTop / 5)
                    document.documentElement.scrollTop = document.body.scrollTop = that.scrollTop + ispeed
                    if (that.scrollTop === 0) {
                        clearInterval(timer)
                    }
                }, 16)
            },
            // 为了计算距离顶部的高度，当高度大于60显示回顶部图标，小于60则隐藏
            scrollToTop () {
                const that = this
                let scrollTop = window.pageYOffset || document.documentElement.scrollTop || document.body.scrollTop
                that.scrollTop = scrollTop
                if (that.scrollTop > 0) {
                    that.btnFlag = true
                } else {
                    that.btnFlag = false
                }
            },
        }
    }
</script>

<style lang="scss">
  #page {
    width: 100%;
    height: 100%;
    overflow: hidden;
  }

  .backTop{
    position:fixed;
    bottom:10px;
    right:45px;
    width: 23px;
    height: 23px;;
    background: url('../../assets/toTop.png');
    cursor: pointer;
  }
</style>
